1. Field of the Invention
The present invention is generally related to a shifting mechanism for a marine drive unit and, more particularly, to a mechanism with a shift linkage which facilitates the movement of the shift linkage and connected components from forward to neutral gear positions, reverse to neutral gear positions, and into either forward or reverse gear positions from a neutral gear position.
2. Description of the Prior Art
Many different types of marine drive shift mechanisms are well known to those skilled in the art. U.S. Pat. No. 5,829,564, which issued to Meisenburg et al on Nov. 3, 1998, discloses a marine drive shift mechanism with chamfered shift rings, stepped cams, and a self-centering clutch. The marine drive shift mechanism includes a shift ring having a chamfer zone along an arcuate portion of its outer circumference facilitating ease of shifting. A stepped camming surface provides step function shifting movement. Neutral positioning notches are provided on the clutch sleeve to improve clutch sleeve placement when the shift mechanism is in neutral.
U.S. Pat. No. 4,679,682, which issued to Gray et al on Jul. 14, 1987, discloses a marine drive shift mechanism with a detent canister centered neutral. The marine drive is provided with a shift mechanism including a detent canister assembly. A cylindrical canister contains a ball biased by a pair of concentric springs into engagement with a shifter lever arm to center the latter in a neutral position. The canister assembly is a self contained modular unit inserted into the marine drive housing. The cylindrical canister has a left end wall with an aperture therethrough and has an open right end containing the ball. The first spring bears at its right end against the ball and extends axially leftward through the aperture in the left end wall of the canister and bears at its left end against the housing. The second outer concentric spring bears at its right end against the ball and is entirely within the canister and bears at its left end against the left end wall of the canister. Upon axial leftward depression of the ball by the shift lever arm, the first inner spring compresses and the canister moves axially leftward until the left wall of the canister strikes the housing wall to close a tolerance accommodating gap, whereafter both springs compress during further leftward depression of the ball. Particular constructional details of the shift lever arm are also disclosed.
U.S. Pat. No. 4,630,719, which issued to McCormick on Dec. 23, 1986, discloses a torque aided pulsed impact shift mechanism. A cone clutch sleeve on a main shaft is moved axially between forward and reverse counter-rotating gears by a yoke having mirror-image oppositely tapered cams on opposite sides thereof which are selectively rotatable to engage eccentric rings on the forward and reverse gears. This engagement drives the yoke away from the one engaged gear and toward the other gear to in turn drive the clutch sleeve out of engagement with the one gear such that torque applied through the cam engaged gear ring assists clutch disengagement of the one gear such that requisite shift force decreases as speed and torque increases. The eccentric face surface of each ring actuates the yoke and drives the sleeve member out of engagement with the one gear and into engagement with the other gear with a pulsed impact hammer effect due to the eccentricity of the face surface as it rotates in a circumferential plane about the main shaft.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In marine drive transmissions similar to those described in the referenced United States patents, the various components of the marine drive unit must move from a neutral gear position to either forward or reverse gear positions as the transmission is shifted by an operator. As the various components move between these distinct positions, they pass through intermediate positions in which the shifting components are not completely in any specific gear position. In other words, as the transmission moves from a neutral gear position to a forward gear position, it must pass through intermediate and possibly indeterminate positions which are neither the neutral nor the forward gear positions. Similarly, as the transmission components move from a neutral gear position to a reverse gear position, they also must pass through intermediate positions which are neither the neutral nor the reverse gear positions. As the marine drive unit components move through these intermediate positions, certain disadvantageous conditions can occur, such as rapid oscillation between neutral and either forward or reverse gear positions. This rapid oscillation can cause a chatter noise and could possibly have a deleterious effect on the various components of the marine drive unit.
It would therefore be significantly advantageous if an improvement could be provided for a marine drive unit which aided the movement of the components from one gear position to another gear position in order to more quickly pass through the intermediate positions.
A marine drive unit made in accordance with the preferred embodiment of the present invention comprises a housing structure and a shifter shaft supported within the housing structure. The shifter shaft is rotatable about an axis and movable along the axis. The axis is generally vertical. A shift linkage has a depression formed in its surface.
The shift linkage is rigidly attached to the shifter shaft, whereby rotation of the shift linkage relative to the axis causes the shifter shaft to rotate about the axis into at least three alternative rotational positions about the axis.
A detent assembly is mounted in the housing and it comprises an insert member and a biasing member. The insert member is urged into engagement with the depression formed in the surface of the shift linkage. In a preferred embodiment of the present invention, the insert member is a spherical ball and the ball is urged toward the surface of the shift linkage by a spring which serves as the biasing member. This urging of the ball into the depression in the surface of the shift linkage centers the shift mechanism into a preselected one of the three alternative rotational positions about the axis. The insert member, or ball, is inhibited by the housing from moving in a direction parallel with the axis of the shifter shaft.
A groove is formed in the surface of the shift linkage. The groove extends along a path in the surface of the shift linkage which intersects the depression. The groove is nonperpendicular to the axis of the shifter shaft and is shaped to receive the insert member in sliding or rolling relation within the groove when the shift linkage is rotated about the axis away from the preselected one of the three alternative rotational positions about the axis. The nonperpendicular relationship between the groove and the axis permits the insert member to remain within the groove, under urging by the biasing member, as the shift linkage rotates about the axis and moves in a direction parallel to the axis in coordination with the shifter shaft.
In a particularly preferred embodiment of the present invention, the depression is generally circular in cross section with a concave surface that is a portion of a sphere. The shift linkage comprises a head and an arm which extends away from the head in a direction away from the shifter shaft.
The insert member can have a spherical surface to facilitate its movement into and out of the depression and, in some embodiments, the insert member can be a ball. The three alternative rotational positions about the axis comprise a forward gear position, a reverse gear position, and a neutral gear position. The preselected one of the three alternative rotational positions about the axis is the neutral gear position. This preselected one of the alternative rotational positions is the position at which the ball is received in the depression within the surface of the shift linkage. The groove, in a preferred embodiment of the present invention, has a rounded bottom surface shaped to conform with the generally spherical surface portion of the insert member.